I'm working on a calculation of diesel exhaust system back pressure and was wondering if there were any values for gas densities and viscosity? Or are the properties for air at exhaust temperatures close enough?
For the products of lean/stoich combustion (e.g. your average diesel and/or gas these days), the mean molecular weight is that of air (28.8 ish). No need for compensation. However, Cp will vary if you are doing compressible flow calc.
My Pratt & Whitney Aeronautical Handbook has gas properties for the combustion products of paraffin hydrocarbon (CH(2n+2)) in air and at 100% theoretical air (stoichiometric), 200% theoretical air (probably close to actual diesel engine operation at rated power), and 400% theoretical air.
The info is used by turbine engine engineers, and my guess is that you should look for turbine engine data resources to get similar data.